Electron-tube circuit



June 17, 1930. HULL 1,764,206

ELECTRON TUBE CIRCUIT Filed April 13, 1928 ml union Ill 4 4 4 7 cl C c, l

Patented June 17, 1930 UNITED STATES PATENT OFFICE LEWIS M. HULL, OF MOUNTAIN LAKES, NEW JERSEY, ASSIGNOR TO RADIO FREQUENCY LABORATORIES, INCORPORATED, OF BOONTON, NEW JERSEY, A CORPORATION OF NEW JERSEY Application filed April 13,

This invention relates to electrical circuits such as electrical amplifier circuits or the like, and especially to such circuits of the type employing electron or vacuum tubes. These tubes may include a closed vessel, an emitting o commonly known as audions, triodes, tet

cathode or other electron-supplying element, an anode or plate, and one or more additional elements or control means which usually take the form of grids or the like. Such tubes are a tube. Such retroaction or regeneration may be .due to capacitive coupling between the output andinput circuits referred to, and in part at least to capacities between the elements of the vacuum tube and their associated connections and external circuit elements, such capacitive coupling residing particularly between the anode and the control element or grid of the tube.

Referring now tothe drawings: Figure 1 represents diagrammatically an electrical amplifier stage embodying my invention as applied to a three electrode tube of standard type. Figure 2 shows an alternative form of such an electrical circuit." Figure 3 shows a cascaded or multi-stage electrical amplifier circuit according to my invention. Figure 4 shows a cascaded or multi-stage electrical amplifier circuit employing four-electrode or double-grid tubes.

Referring now to Figure 1,VTrepresents a. three electrode vacuum tube including anode or plate P, emitting cathode or filament F, and control means or grid G. A plate coil L is connected between anode and cathode in series with B-battery B, and may form the primary of an output transformer L Ii having its secondary tuned by a variable condenser C The lower terminal of this tuning condenser may be grounded as shown. Between the grid, G, and cathode, F, is connected a coil L which may constitute the secondary of an input transformer L --L The ELECTRON-TUBE CIRCUIT 1928. Serial ml zeasor.

coil L is wound or connected in the reverse sense with respect to the coil L so that when an oscillatory current flows in the tuned circuit L L C the oscillating voltage of ter'minal'2 of coil L with respect to ground, is substantially opposite in phase to the voltage of the grid G with respect to the grounded cathode F.. Inseries with the coil L is connected a coil L. which may in certain instances be coupled to the coils L and L Ordinarily, however, the coil L has negligible or substantially zero electromagnetic coupling with the coil L Incertain physical embodiments of this circuitI prefer to arrange the coil L at right angles to the coil L so as to produceneghgible electromagnetic coupling between them and the form on which coil L is wound maybe supported by or within either the form on which coil L or that on which coil L is wound. In series with the coils L L is connected the variable condenser 0 a resonant input circuit for the amplifier stage thus being formed. The

low potential side of this tuningcondenser may also be grounded, as shown. When it is desired to impress an incoming signal or other oscillatory voltage upon the amplifier circuit, this may be done in a variety of ways. In the particular embodiment shown in Figure 1, the input voltage, for example that derived from the plate circuit of a preceding tube or from an antenna system, may be applied between the input terminals 1 and 2, that is, across the coil L as shown. Thus, in Figure 1 the input to the amplifier circuit is represented as an oscillatory voltage in series with a resistance (the equivalent of the plate circuit of a vacuum tube) connected across the input terminals. A balancing condenser C0 is connected between the junction of the coils L and L in the tuned input circuit and the anode of the tube, as shown. This balancing capacity ordinarly takes the form of a physical condenser, although any suitable capacitive impedance, including the natural capacities of the circuit, may beemployed. In this diagrammatic represcnta- V I tion the A, B and C batteries are represented in the conventional manner, each being supplied with a by-pass condenser C if desired. However, these batteries may of 1 course be replaced by socket power devices, or by an alternating current supply to the cathode or filament, as is now well understood in this art.

Figure 2 represents a single stage of an electrical amplifier circuit similar to that of Figure 1, except that the input voltage is impressed upon the tuned input circuit L L C by means of a quarternary coil L coupled to the coil L The input terminals 1 and 2 are represented as before.

In each of the herein-described modifications, it is of course understood that the amplifier stages may be cascaded in any suitable manner, and that the input and output circuits may be arranged or modified accordingly.

Figure 3 shows one such cascaded or multistage arrangement employing essentially the circuit of Figure 1. The firsttuned circuit L L C (shown at the left hand side of the drawing) represents the input circuit of the amplifier, and may, for example, be

coupled in any desired manner to 'a receiving antenna, loop, or the like, in cases where the amplifier is used in a radio receiving system. The output of the first stage, (i. e. tube #1) is connected across the coil L3 between the input terminals 1 and 2, in the tuned input circuit of the second stage (i. e. tube #2). The circuit is otherwise arranged substantially as before.

Figure 4 represents a cascaded or multistage arrangement employing tubes of the double grid type. Since these tubes are frequently of the so-called high-mu or high impedance. type, I sometimes find it more appropriate to connect theanode and cathode terminals of the tube directly across the tun ing condensers C as shown. For example, when tube #1 in the first stage has a plate impedance of the order of 250,000 ohms. it is appropriately connected across the tuning condenser C of the tuned input circuit.L L '-C of the second or succeeding stage, this tuned circuit of course constituting the tuned output circuit of the first stage as well as the input circuit of the second stage. The

plate impedanceof tube #1 and the imped-- ance of the tuned circuit L L C at resonance, may be made large, in order to obtain maximum amplification, or the impedance of the tuned circuit at resonance may be made slightly lower than the plate impedance of tube #1 in order to gain increased selectively without substantial sacrifice of amplification, as is well known in this art. The foregoing observations as to the impecance of the tuned circuit with relation to the output impedance of the associated tube apply also to the other circuits here illustrated. In general, when the tube is of relatively low plate impedance I prefer to connect or couple the plate circuit of the tube across a part only of the tuned circuit L L C into which the tube works, for example across the coil L as shown in Figures 1 and 3, or across the coil L coupled to the coil L as shown in Figure 2. On the other hand, when the tube has a relatively high plate impedance, the input to the tuned circuit is preferably across the tuning condenser C i. e. across the whole circuit, in order that the plate impedance of the tube and the impedance of the tuned circuit into which it works may be substantially equated, as shown in Figure 4.

I In circuit arrangement-s employing four electrodctubes of the double grid type, such as that shown in Figure 4, the input is ordinarily connected between the inner or control grid G and the cathode F, while the outer, or as it is sometimes called emission shield grid, G is given a positive bias. This may be done by connecting the grid G to the B battery B as indicated, or in any other suitable manner, including the use of a separate battery or other source of potential for this purnose. A tube employed. in this manner may be either of the completely shield type in' which the grid G almost completely surroundsthe anode, or of the partially shielded type. In the particular arrangement shown in Figure 4 the tubes are of the former or completely shielded type.

In the case of a four electrode tube of the double grid type. if the tube constants are properly chosen, however, the input may be connected between the cathode and the outer grid, G i. e., the grid next the anode, this grid then serving as the control element,

while the other grid, G is given a positive bias in any suitable manner, as iswell understood in connection with the operation of four electrode tubes according to the space charge method.

I shall now give certain specific examples of suitable constants for circuits arranged according to my invention, the circuit constants being illustrative only of constants which I have successfully used in practice.

In a circuit similar to that illustrated in Figure 1, I have successfully used the following constants -L =80turns of #32 wire closely wound on a 1 form.v V I L =8O turns of enameled wire on a 1% form, the turns being spaced.

L =8O turns of #32 enameled wire closely wound on a 7 form.

L -L,=a standard'amplifier transformer having 12 turns on an extended primary fitting closely inside a secondary composed of 10% turns of #32 wire wound on a 1 form.

The balancing capacity Co was approximately 20 micro microfarads.

The overall amplification of the stage was found to vary from about 30 to 6.00, over the usual range of frequencies.

A specific example of certain circuit constants which I have used successfully in connection with a double grid tube of the type shown in Figure 4 is as follows:

L =lO0 turns #30 enameled wire closely wound on a 1 A form.

L =74 turns #38 silk-covered wire, space wound on a 1" form.

L =lO turns on a 7; form.

The circuit arrangements and diagrams illustrated and described above, and the particular circuit constants given, are merely specific examples of embodiments of my invention. Many variations and modifications of the circuits and arrangements hereindescribed fall within the scope of my invention.

I claim:

1. An electrical circuit comprising, in combination, an electron tube including at least an electron-emitting cathode, an anode, and a control element; an output circuit for said tube associated with the anode and cathode thereof; a tuned input circuit including, in series, a coil arranged to impress input voltage between the control element and cathode of said tube, a second coil connected to said first coil but having negligible electromagnetic coupling therewith, and a tuning condenser connected across both of said coils in series; a connection from one point in said tuned input circuit to ground; and capacitive impedance arranged between said anode and a point in said tuned circuit at which the alternating current potential is substantially difi'erent from that of said grounded point; whereby said electrical circuit may be balanced to cause the flow of compensating currents through said capacitive impedance of the proper phase to oppose undesired retroactive currents due to capacitive coupling between said output and input circuits.

2. An electrical circuit comprising, in combination, an electron tube including at least an electron-emitting cathode, an anode, and a control element; an output circuit for said tube associated with the anode and cathode thereof; an input circuit including a coil connected between the control element and cathode of said tube, a second coil coupled to said first coil in the reverse sense, a third coil connected in series with said second coil but having negligible electromagnetic coupling therewith; and capacitive impedance between said anode and the junction of said second and third coils.

3. An electrical circuit comprising, in combination, an electron tube including at'least an electron-emitting cathode, an anode, and a control element; an output circuit for said tube associated with the anode and cathode thereof; an input circuitincluding a coil connected between the control element and cath ode of said tube, a second coil coupled to said first coil in the reverse sense, a third coil connected in series with said second coil but having negligibleelectromagnetic coupling there-. with, and a tuning condenser connected across said second and third coils in series to form atuned cir'cuitincludingsaid second and third (3011s and sald tunlng condenser and a balancing capacity connected between thej unctionof said secondand third coils and the anode of said tube; whereby said electrical circuit may be balanced to reduce efiects other than those dip); to desired forward repeater action of said tu e. v 4:. An electrical circuit comprising, in combination, an electron tube including an electron emitting cathode, an anode, a con trol grid, and a second grid; an output circuit associated with the anode and'cathode of said tube; a tuned input circuit including, in series, a coil arranged to impress input potential between the control element and cathode of saidtube, a second coil connected in series with said first coil but having negligible electromagnetic coupling therewith,

and a tuning condenser connected across both. of said COllS in series; a connection from one point in said tuned input circuit to ground; a capacitive impedance arranged between said anode and a point in said tuned circuit at which the alternating current potential is substantially different from that of said grounded point whereby said electrical circuit may be balanced to cause the flow of compensating currents through said capacitive impedance of the proper phase to oppose undesired retroactive currents due to capacitive coupling between said output and input circuits; and means for imparting a positive bias to said second grid.

5. An electrical circuit comprising, in combination, an electron tube including at least an electron-emitting cathode, an anode, a control grid, and a second grid; an output circuit associated with the anode and cathode of said tube; an input circuit including a coil connected between the control grid and cathode of said tube, a second coil coupled to said first coil in the reverse sense, a third coil connected in series with said second coil but having negligible electromagnetic coupling therewith, and a tuning condenser connected across said second and third coils in series; a capacitive impedance connected between the anode of said tube and the junction of said second and third coils; and means for imparting a positive bias to said second grid.

6. A multi-stage electrical amplifier comprising a plurality of electron tubes arranged in cascade and each including at least an electron emitting cathode, an anode, and a control element; a coupling system interposed between two of said cascaded tubes and includinga coil connected between the control element and cathode of the second of said tubes to form a secondary of a coupling transformer, a second coil coupled to said first coil in the reverse sense and constituting a primary oi said coupling transformer, athird' coil connected in series with said second coil but having negligible electromagnetic con- 7 pling therewith, a tuning condenser connected across said second and third coils'in series to form a tuned circuit including said. second and third coils and said tuning condenser, and means for impressing the output Voltage of the first of said, tubes upon said tuned 10 circuit; and capacitive impedance connected between the junction of said second and third coils and the anode of the second of said tubes; whereby the electrical amplifier circuit including the second of said tubes may be balanced to reduce effects other than those dug to desired forward repeater action of said tu e.

V In testimony whereof, I afllx my signature. LEWIS M. -HULL. 

